n-Butyl nitrite is useful agent for nitrosation. It can for example be used for the preparation of diazonium residue containing compounds from primary amines.
US 2003/149292 A1 discloses a method for preparing alkyl nitrites RONO wherein R represents a C1-20 linear or branched alkyl group; the method consists in gradually and continuously adding in an aqueous medium, an alcohol ROH, a nitrite MNO2, wherein M represents a metal cation, and a strong acid, so as to form continuously said alkyl nitrite, and in continuously drawing off said alkyl nitrite thus formed from the reaction medium. Of the two examples 1 and 2, only example 1 concerns the preparation of n-butyl nitrite, the example discloses a residual n-butanol content in thus prepared n-butyl nitrite of 1.7 to 1.9% (GC), the purity of the n-butyl nitrite is 97 to 98%.
WO 03/014059 A1 discloses a process for continuous preparation of alkyl nitrites and alkyl dinitrites by reaction of an alkanol or a dialkanol with an inorganic nitrite in the presence of at least one mineral acid that does not oxidize nitrite, wherein    (i) the alkanol or dialkanol is mixed with an aqueous solution of the mineral acid using on average not more than 1.01 mol of acid equivalents per mole of hydroxyl group in the alkanol or dialkanol,    (ii) an aqueous solution of the inorganic nitrite is added continuously to the aqueous mixture obtained in (i) in a reaction zone, and    (iii) the organic phase is optionally isolated.
Purities from 98.62% to 99.02% (GC) are reported. Residual butanol content was from 0.77% to 1.01%.
There was a need for a process with high yield of n-butyl nitrite and simultaneously with a low content of n-butanol of 0.7% or lower (GC area %). A low content of residual n-butanol is important because the residual n-butanol interferes in following reactions where the n-butyl nitrite is used as substrate.
Furthermore the process should work with shorter reaction times and/or shorter residence times.
Surprisingly it was found that an increase of the amount of acid improves the yield and lowers the residual content of n-butanol in a continuous reaction. This was unexpected since WO 03/014059 A1 expressly stresses the need for a low amount of acid.
In the following text, if not otherwise stated, the following meanings are used:
ambient pressure usually 1 bar, depending on the weather;
BUOH n-butanol, n-BuOH;
BUONO n-butyl nitrite;
Ex example;
CE comparative example;
RETI residence time;
wt % percent by weight, weight-%, wt-%.